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Help, sensor hell!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Mudfreak, May 20, 2001.

  1. Mudfreak

    Mudfreak 1/2 ton status

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    MY 89 k5 seems to have a massive air leak coming from around the throttle body, but I can't seem to find it. Also I'm getting a code for the TPS. The sensor was replaced about 6 months ago. The engine idles like a drag truck with a heavy cam in it, and wants to stall out. The O2 sensor is new, the MAP sensor is new, the EGR is about 6 months old, Any ideas on what is causing me to get a code and cause my engine to run crappy would be greatly appreciated. Thanks

    [​IMG]
     
  2. rich'90

    rich'90 1/2 ton status

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    try the idle air control valve. it mounts in the throttle body on the passenger side rear. could be your problem, your truck will idle like crap if it is bad.
    good luck

    Go heavy or Go home[​IMG]
     
  3. Gandolf

    Gandolf 1/2 ton status

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    You say you have a massive air leak. I must assume you mean a vacuum leak. Keep looking for the leak because this is the problem and it must be corrected. You also say you are getting a code for the TPS - Throttle Position Sensor. The TPS is a purely electrical part, so there are no vacuum connections to it. Double check the code and make sure this is the correct item you are getting the code on.
    If you are sure it is giving a code for the TPS, then this is another problem. Get a Digital Volt Meter and test the TPS. Use the DC Volt Scale. There are 3 wires that go to the TPS. With the ignition ON and engine OFF, test the two outside wires (Black and Grey)...you should get close to 5.0 volts. Then check the Dark Blue center wire with the Black wire. This reading should be between 0.5 to 1.2 volts with the throttle closed. Keep this connected and slowly open the throttle. As you increase the throttle, the voltage will increase. Do this slowly and cover the whole range up to full throttle. The voltage should increase smoothly thru the whole throttle range. The TPS is like the volume control on your radio where you will hear bad spots in the volume control as scratchey sounds in the speakers. On this test, you are looking for any bad spots and you will "see it" because a bad spot will cause the voltage to jump around. If the TPS fails any of these tests, it must be replaced. When you are done, clear the code by disconnecting the battery for a minute or two. This is the best help I can give you with the information you furnished. Good Luck

    '89 K5 Silverado..."You can’t have a real adventure, unless the outcome is truly uncertain".
     
  4. WOODYJ

    WOODYJ 1/2 ton status

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    There is a sure way to find an air leak if you have one. Get a can of spray brake cleaner or contact cleaner. Be sure that it is NOT FLAMABLE!!! Spray it around your intake and throttle body. When the engine sucks any of this in it will change it's running characteristics. You can really find air leaks this way!! Just be sure the spray is not flamable!!

    k5woody I Don't Understand The Jeep Thing Either!!!
     
  5. Twiz

    Twiz 1/2 ton status

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    To all T.B.I., F.I. or anyone with some time on their hands.

    I swipped, ahh, I mean borrowed our G.M. service manual for 1992 T.B.I. trucks. I'm thinking about putting up a post with some discripsions and possible codes, stuff like that. Is this a good idea? Would it be usefull in the future? Maybe tag it or print it up- for future use. It would look something like this;

    Throttle Position Sensor (TPS)
    TPS connected to the throttle shaft. It is a potentiometer, with one end connected to 5 v. from the ECM, one to ground, one guns back to the ECM to measure voltage from the TPS. As the throttle opens the output increases to a max of aprox 4.5v. The ECM uses this input to determine fuel delivery

    Then continue on to the next sensor. I'm gong to keep it knida basic, just the meat and potatos- no gravy, cause that would be a hell of alot of typing. Just an idea.

    By the way, Sounds like a vacume leak to me. Any leak below the throttle blades on a F.I. engine will cause the idle to be sky-high. Someone already sugjested this. Not sure about the TPS code thow, but Grandolf sounds dead on for the diag. on it.

    Twiztid

    Edited- Sorry, I din't mean to swipe -er- borrow your post, Its just a thougt. I'll keep reading the S.M., do you have a code number?<P ID="edit"><FONT SIZE=-1>Edited by Twiztid on 05/20/01 08:26 PM (server time).</FONT></P>
     
  6. Mudfreak

    Mudfreak 1/2 ton status

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    Thanks for the info, got the air leak sound fixed, I replaced the IAC with a spare one that I had when I purchased a stock GM throttle body from the junk yard with injectors and all the sensors on it for $40. This seemed to cease the air leak sound, but still runs rough, I cleared the codes and haven't gotten any more codes but still not quite 100% yet. Any other Ideas?

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  7. jarheadk5

    jarheadk5 1/2 ton status

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    Maybe a bad plug wire is causing you to drop a cylinder intermittently. Wait till dusk/dark, use a spray bottle of water and lightly mist near the plug wires. If you see an arc, you've got a bad plug wire. OR, if you have a timing light, hook it up to the battery and put the pickup on all your plug wires and watch the light. If the light is intermittent on one wire, that's your bad one.
    BE CAREFUL doing either of these!! No loose clothes, watch the timing light leads carefully.

    As for the air leak, you must have some real good hearing, because my truck's got WAY too much underhood noise for me to ever find an air leak by sound alone. The carb cleaner trick is great, plus it cleans as you troubleshoot!!

    <font color=red>Click those banners and help support CK5!!<font color=black>
    [​IMG] Semper Maintenance!
     
  8. rich'90

    rich'90 1/2 ton status

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    glad the IAC fixed the leak, thought it might be that. did you reset the value after installing it? if you just started it up and let it run, it is still in the same position. I can't remeber the exact speed but I think you have to drive it over 40mph so it goes all the way in and it resets it initial value. After that go back and try starting it again and see what happens. Oh, disconnect the battery first before you go for about 1min.
    Good luck

    Go heavy or Go home[​IMG]
     
  9. prjt_blzr

    prjt_blzr 1/2 ton status

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    Thought I'd share a thought on the carb cleaner. I used this trick for a lot of years and never had a problem. Until working on my dad's '96 pickup. I thought I'd found a vacuum leak at the rear of the manifold. On the second squirt I found out that it was a bad plug wire. Yeah, you guessed it lots of flames and it started an engine fire!! Good thing I keep a fire extinguisher handy. It only burnt a vacuum harness. Use a non-flammable degreaser if possible. Otherwise a fire extinguisher is a handy thing to have.
     
  10. bart

    bart Registered Member

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    Check the Manifold Absolute Pressure Sensor...it hooks to the rear of the tbi with a hard vacuum line. This reads vacuum and helps the computer set mixture, etc.etc...check this line for cracks...new sensors are about $20.

    I had a similar problem with a 89 K5 when I accidentially pulled this line off of the back of the TBI...it could be cracked though.

    bart
     
  11. bart

    bart Registered Member

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    oops, I see you already replaced the map sensor...you say you are getting a code for the tps...what is the code number you are coming up with?

    put a vac gage on the manifold...anything under 18 in Hg is bad at idle.

    try disconnecting the vac to the accumulator sphere...it runs the vac accessories.

    A computer scan tool is really helpful for working on the GM TBI systems...there is one made by an small company in Colorado, the company is TDS technologies...it's called TurboLink..about $150 with software and interface...gives you a display of the computer data and has logging capabilities as well.

    A GM shop manual is worth its weight in gold.
     
  12. Mudfreak

    Mudfreak 1/2 ton status

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    I was getting a code 22, 33 and 45, but after putting the IAC off my parts throttle body and the MAP sensor,it took care of all the codes. I found the air leak because I was checking all the bolts on the ERG, Throttle body and everything that had a gasket under it to make shure it was tight and torqued to the right settings. Thanks for the info on setting the valve on the IAC I was'nt aware of having to drive it over a certain speed , but that makes sense.Only prob with that is that I was taking it to my buddy's trans shop to get the trans fixed when the engine decided it would act up.

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